In the event that lands lie within both a fire protection district and a forest protection assessment area they shall be taxed and assessed as follows:
(1) If the lands are wholly unimproved, they shall be subject to forest protection assessments but not to fire protection district levies;
(2) If the lands are wholly improved, they shall be subject to fire protection district levies but not to forest protection assessments;
(3) If the lands are partly improved and partly unimproved they shall be subject both to fire protection district levies and to forest protection assessments: PROVIDED, That upon request, accompanied by appropriate legal descriptions, the county assessor shall segregate any unimproved portions which each consist of twenty or more acres, and thereafter the unimproved portion or portions shall be subject only to forest protection assessments.